From: Peter Hurley <peter@hurleysoftware•com>
To: Oleg Nesterov <oleg@redhat•com>
Cc: Sree Harsha Totakura <sreeharsha@totakura•in>,
linux-kernel@vger•kernel.org, netdev@vger•kernel.org,
"Eric W. Biederman" <ebiederm@xmission•com>
Subject: Re: pppd service crash in linux-3.13.6
Date: Sat, 15 Mar 2014 08:49:37 -0400 [thread overview]
Message-ID: <53244C61.5090508@hurleysoftware.com> (raw)
In-Reply-To: <20140314210456.GA19032@redhat.com>
On 03/14/2014 05:04 PM, Oleg Nesterov wrote:
> On 03/14, Peter Hurley wrote:
>> On 03/14/2014 03:23 PM, Oleg Nesterov wrote:
>>> On 03/14, Peter Hurley wrote:
>>>>
>> Yes, cgroup_release_agent() is the work function that is scheduled.
>>
>>>> which requires both namespace and tty facilities.
>>>
>>> Hmm... why?
>>>
>>> The exiting task obviously can't exec. The only way to spawn a userspace
>>> process is call_usermodehelper(), it should work just fine, no?
>>
>> You're correct, in the immediate sense that the user command exec'd will
>> not inherit open file descriptors.
>>
>> But what if it expects to be able to find the intact children of
>> the foreground process group, and can't because the controlling tty
>> has already been torn down and all the children already sent SIGHUP.
>
> Which group/tty ? call_usermodehelper() asks the workqueue thread
> to kthread_create/exec. See also below...
>
>> Or what if the user command expects to find and join the user namespace
>> of the dying process but now it's already been freed?
>
> But it can't even know who called call_usermodehelper(). Besides,
> cgroup_release_agent() uses UMH_WAIT_EXEC, so the caller can continue
> and disappear completely before the usermode process has any chance
> to do something.
I'm just hypothesizing potential breakage, since the order of teardown
is sensitive to changes, and I didn't do a complete audit of all the
possibilities.
If you feel strongly about moving disassociate_tty(), I won't object.
Regards,
Peter Hurley
next prev parent reply other threads:[~2014-03-15 12:49 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <531A37FF.4000509@totakura.in>
2014-03-10 16:56 ` pppd service crash in linux-3.13.6 Sree Harsha Totakura
2014-03-10 19:23 ` Peter Hurley
2014-03-13 17:06 ` Oleg Nesterov
2014-03-13 17:55 ` Peter Hurley
2014-03-14 14:19 ` Peter Hurley
2014-03-14 15:02 ` Peter Hurley
2014-03-14 19:23 ` Oleg Nesterov
2014-03-14 20:28 ` Peter Hurley
2014-03-14 21:04 ` Oleg Nesterov
2014-03-15 12:49 ` Peter Hurley [this message]
2014-03-17 18:04 ` [PATCH 0/2] (Was: pppd service crash in linux-3.13.6) Oleg Nesterov
2014-03-17 18:04 ` [PATCH 1/2] exit: call disassociate_ctty() before exit_task_namespaces() Oleg Nesterov
2014-03-17 18:05 ` [PATCH 2/2] exit: move check_stack_usage() to the end of do_exit() Oleg Nesterov
2014-03-10 19:54 ` pppd service crash in linux-3.13.6 Ben Hutchings
2014-03-12 21:25 ` Sree Harsha Totakura
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